We have Axis Ultra DLD from Kratos which performs very well. You might want to have a look at this instrument especially if energy resolution is an issue.

I recommend that you evaluate specific factors. Each vendor has its own means to handle charge neutralization, "small spot" analysis, sample input/output/mounting, large sample analysis, and angle resolved analysis. In my experience, the stability, reliability, ease-of-use, and long-term performance of these factors are key. No one vendor has cornered the market on a top of the line system across all of these factors.

Create a table with vendor as the first column and each of the factors as additional columns. Document how each is handled. For example, with a PHI VP, the "small spot" is done by rastering electrons on a filament while Kratos focuses the lens on the sample (I believe). Do this for all factors. Then, ask each vendor to address the pros and cons of their method versus the other methods. By example ... What are the long term issues with using a filament for small spot versus focusing the lens (you have to replace the filament in the one case and you do not in the other)? What are the pros (the filament method may give higher S/N and smaller spot size)? Rank each factor as to its importance for the clients you anticipate. Do you really need angle-resolved analysis or large sample analysis? Will you be satisfied without chemical mapping analysis, and if not, can this be added later?

An additional factor is to ask for output specifications from each instrument. The best approach here is to have a set of typical samples that can be run by each vendor on the instrument that you want. I recommend gold, teflon, and highly oriented pyrolitic graphite (HOPG) as three base comparisons. Ask the vendors to provide appropriate survey and high resolution scans. Get all of the factors for those scans ... range, dwell time, sweeps, pass energy, spot size, take off angle, and so forth. Sit down with the results and determine the S/N and resolution. Ask the vendors to provide the binding energy plot of output versus theory across the BE range (i.e. the binding energy calibration of the instrument). Ask for the typical transmission function behavior of the analyzer. The critical issue to avoid here is buying a system that has high S/N in survey for composition analysis but degrades in S/N or resolution on high resolution scans (due to the way the lens operate).

I also recommend that less is better. Avoid the promise of getting extra gadgets at reduced costs as add ons. Typically those components are the knock-off brands that a vendor is trying to add at significant mark-up. As needed, extract a promise to honor the cost of the add-on for a year and allow yourself time to consider its true value. Or insist on the next level up in component quality with the same reduced cost factor.

My final recommendation is to get a promise from the vendor in writing to stand firmly behind the warranty on their system for at least a year after install AND stand behind the promised delivery date. Insist that warranty issues will result in free service visits within a week and delays will result in cost reductions by some factor. I have heard stories from each vendor of instruments that are promised and not delivered in reasonable times and instruments installed that do not work well over the first year with agonizing delays to get service visits.

I must end on a positive note. While none of the vendors have cornered the market across all factors of concern, all of them have instruments that work very well by most standards. The key is to know up front what you are getting as potential issues or downsides. You will want to buy a system to last and be used to its fullest potential for over a decade or more by everyone in your group, company or university, not just be used on occasion over a few years by you alone.

Best regards in your considerations.

Hello Jurgis, first of all, the choice of the best instrument is strongly affected by the samples you going to study. I have an experience with both Kratos and Phi instruments.

The main advantage of Kratos instruments is high sensitivity. This is essential for the samples with low content of the element of interest. This high sensitivity is achieved for the large analysis area (about 600x800 microns). The sensitivity level in some cases may be as low as 0.01 at%. But for the ferromagnetic samples you may not be able to use magnetic lens which reduces the element sensitivity approx. by 10 times. Kratos neutralization system provides a reliable neutralization and a good energy resolution for non-conductive samples even for the large analysis area. But from my experience for some samples it may be tricky to find optimal parameters for the neutralizer.

The sensitivity of Phi instruments is lower comparing to Kratos instruments. For the largest possible analysis area in each spectrometer (with the same acquisition time and pass energy) you will get noisier spectra using Phi spectrometer comparing to the Kratos instrument. But if you are interesting in the small spot analysis (let's say less than 50 microns) the Phi instrument becomes more sensitive. Dual beam neutralization system of Phi instrument works very good. I have never tuned it for the particular sample. Due to the rastering of the X-ray beam, localization of area of interest is very simple. The ion gun in Phi instruments is better focused providing more flat ion beam which is essential for depth profiling.

In my opinion, Phi instrument is better for small size analysis and depth profiling. At the same time, if you need a high sensitivity for the large analysis area Kratos instrument will be better choice.